Entity FrameWork relationship many x many extra field

In this case, you need a type to set this extra value, making it impossible for you to have direct access from your Person or Course class.

You can treat this relationship as a new Entidade de Agregação , since this information will be relevant to the relationship.

However, you must perform this entity's manual handling, as well as add a new DbSet<CourseInstructor> in its context.

In your classes Course and Person you should contain a list of CourseInstructor .

For example:

public class CourseInstructor
{
    public int Id { get; set; }

    public int CourseId { get; set; }

    public virtual Course Course { get; set; }

    public int PersonId { get; set; }

    public virtual Person Person { get; set; }

    public string Extra { get; set; }

    public int InstructorId { get; set; }

    public virtual Instructor Instructor { get; set; } 
}

A link that can also help you: Many Relationship For Many Entity Framework 6

Just as Felipe Oriani mentioned the child of a new class "CourseInstructor", but the Entity FrameWork Code First does this automatically I will give an example

        public class Person 
        {
            public Person ()
            {
                this.Courses = new HashSet<Course>();
            }

            [Key]
     [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
public int PersonId{ get; set; }
public strng lastName{ get; set; }
public strig firstName{ get; set; }



            public virtual ICollection<Course> Courses { get; set; }

        }

///

      public class Course 
        {
            public Course ()
            {
                this.Persons = new HashSet<Person>();
            }

            [Key]
     [DatabaseGenerated(System.ComponentModel.DataAnnotations.Schema.DatabaseGeneratedOption.Identity)]
public int CouserId{ get; set; }
public string Title{ get; set; }
//...


            public virtual ICollection<Person> Persons { get; set; }

        }

In this way you create a new table in the database, without having to create a new class. makes it easy for you to change any other class with the same information every time you change any of the class's tabs.

Try this out

    public class Course 
{

     [key]
     public int CourseId {get;set;}

     etc ....

     [ForeignKey("CourseID")]
     public virtual ICollection<Person> Persons { get;  set; }

}


public class Person 
{
    [key]
    public int PersonId {get;set;}

    etc...

    [ForeignKey("PersonID")]
    public virtual ICollection<Course> Courses { get;  set; }
}


public class CourseInstructo 
{
   [key] // de preferencia com autoincremento
   public int CourseInstructoId {get;set;}


   [ForeignKey("PersonId")]
   public virtual Person Person { get; set; }

   [ForeignKey("CourseId")]
   public virtual Course Course { get; set; }

   [Key, Column(Order = 0)]
   public virtual int PersonId { get; set; }

   [Key, Column(Order = 1)]
   public virtual int CourseId { get; set; }

   //Campo extra

}